Clamps are normally required to handle paper rolls of widely-varying diameters in both vertical and horizontal orientations. A typical clamp comprises a pair of clamp arms either slidably or pivotally mounted upon a clamp frame and movable with respect to such frame selectively toward and away from each other to engage or release paper rolls of different diameters.
In the papermaking industry, it is generally known that paper to be converted into a consumer product such as paper towels, bath tissue, facial tissue, and the like is initially manufactured and wound into large rolls. By way of example only, these rolls, commonly known as parent rolls, may be on the order of 10 feet in diameter and 100 inches across and generally comprise a suitable paper wound on a core. In the usual case, a paper converting facility will have on hand a sufficient inventory of parent rolls to be able to meet the expected demand for the paper conversion as the paper product(s) are being manufactured.
However used, the compressive-type clamps, discussed supra, have numerous draw-backs. The most significant of these is the use of a compressive-type clamp for the pick-up and transport of convolutely wound web materials (e.g., a parent roll of paper) is the deformation of the cylindrical surface of the parent roll by the compressive-type clamp.
There are several factors that can contribute to the deformation of a parent roll of paper. First, because of the soft nature of the paper used to manufacture paper towels, bath tissue, facial tissue, and the like, it is common for parent rolls to become out-of-round. Second, not only the soft nature of the paper, but also the physical size of the parent rolls, the length of time during which the parent rolls are stored, and the fact that roll grabbers using these compressive-type clamps used to transport parent rolls grab them about their circumference can contribute to this problem. For example, because the weight of a parent roll is typically quite substantial, the compressive-type clamps must necessarily exert a significant amount of force upon the surface of the roll in order to maintain control of the roll during movement of the roll from one location to another.
As a result, by the time many parent rolls are placed on an unwind stand they have changed from the desired cylindrical shape to an out-of-round shape. An exemplary un-compressed parent roll is shown in FIG. 1A. An exemplary compressed parent roll due to contacting engagement of the parent roll with a compressive-type clamp is shown in FIG. 1B. As mentioned, this artifact of surface deformation is particularly exacerbated upon convolutely wound parent rolls of tissue and towel substrates such as bath tissue and paper toweling. Since these products tend to be of low basis weight and can have decorative surface architectures, any compressive force applied to the surface thereof tends to distort the shape of the parent roll. An out-of-round parent roll may not be perfectly oblong or elliptical but, rather, they may assume a somewhat flattened condition resembling a flat tire, or an oblong or egg-shape, or any other out-of-round shape depending upon the amount of force required to securely hold the parent roll.
Even only slightly out-of-round parent rolls present considerable problems. In an ideal case with a perfectly round parent roll, the feed rate of a web material coming off of a rotating parent roll can be equal to the driving speed of a surface driven parent roll. However, with an out-of-round parent roll the feed rate can likely vary from the driving speed of a surface drive parent roll depending upon the radius at the web takeoff point at any moment in time. If the rotational speed remains substantially constant, the feed rate of a web material coming off of an out-of-round parent roll will necessarily vary during any particular rotational cycle depending upon the degree to which the parent roll is out-of-round. In practice, however, parent rolls are surface driven which means that if the radius at the drive point changes, the rotational speed can also change generally causing variations in the feed rate. Since the paper converting equipment downstream of the unwind stand is generally designed to operate based upon the assumption that the feed rate of a web material coming off of a rotating parent roll will always be equal to the driving speed of the parent roll, there are problems created by web tension spikes and slackening.
Additionally, it is believed that an out-of-round parent roll produces finally wound consumer products having inconsistent desired physical characteristics. Without desiring to be bound by theory, it is believed that a compressive-type clamp used for the conventional pick-up of a parent roll of wound web material effectively removes any caliper that may have been built into the product being produced for the parent roll. It is believed that this lost caliper cannot be recovered to any large degree due to the early stage of the life of the web material that is being so compressed. This lost and unrecoverable caliper can have a deleterious effect on the finally converted web material because the desired target values of the chosen parameters will be out of range even before the converting process has begun. Net—this clearly undesirable effect on the end product can be noticed by an end user of the product.
Regardless of the amount of pressure exerted by the compressive-type clamps on the parent roll, at least one point in the rotation of the parent roll exists where the relationship between the web take off point radius and the parent roll drive point radius that results in the minimum feed rate of paper to the line. At this point, the web tension can spike since the feed rate of the web material is at a minimum and less than what is expected by the paper converting equipment downstream of the unwind stand. Similarly, there can exist at least one point in the rotation of the parent roll where the relationship between the web take off point radius and the parent roll drive point radius results in the maximum feed rate of paper to the line. At this point, the web tension can slacken since the feed rate of the web material can be at a maximum and more than what is expected by the paper converting equipment downstream of the unwind stand. Since neither condition is conducive to efficiently operating paper converting equipment for manufacturing paper products such as paper towels, bath tissue and the like, and a spike in the web tension can even result in a break in the web material requiring a paper converting line to be shut down, there clearly is a need to overcome this problem.
In particular, the fact that out-of-round parent rolls create variable web feed rates and corresponding web tension spikes and web tension slackening has required that the unwind stand and associated paper converting equipment operating downstream thereof be run at a slower speed in many instances thereby creating an adverse impact on manufacturing efficiency.
Thus, there is a long-felt need to provide a better manner for the handling of parent rolls that eliminates the problems experienced and observed by manufactures using current roll-handling technology such as the aforementioned typical compressive-type clamp arms. It would be beneficial if the long-felt need was resolved by equipment that assists in maintaining the desired cylindrical parent roll shape. It would also be beneficial if the new parent roll handling equipment also maintained better control of the parent roll during movement. Further, it would be beneficial if the new parent roll handling equipment provided greater flexibility in the options required by paper product manufacturing operations by providing a more direct interface with the dry end of parent roll production, the ability to manipulate parent roll orientation for parent storage, as well as the ability to manipulate parent roll orientation for insertion of the parent roll into a converting process.